The invention relates to a lead-acid battery having a plurality of individual cells.
A conventional lead-acid battery comprises at least six plate blocks or cells which are connected in series. Each cell has a voltage of approximately 2 volts. When connected in series in a standard starter battery, the cells deliver a terminal voltage of approximately 12 volts.
The cells have a positive electrode contact and a negative electrode contact, the so-called connectors, on their top side. The electrode contacts each comprise comb-like contact elements. A plurality of positive and negative plates are interconnected with the aid of the electrode contacts to form plate sets. The parallel connection of the individual plates results in an increase in surface size, this allowing a higher capacitance and current-carrying capability of the arrangement. The plate sets are pushed one into the other to form a plate block. Each plate block comprises a positive plate set with a positive electrode contact and a negative plate set with a negative electrode contact. A negative plate includes an electrode grid which is composed of lead. The negative grid also has an electrode contact element which is part of the negative electrode contact. The negative plate has an active material layer which is composed of amorphous lead which sheaths the negative grid. A positive plate usually has, if the lead-acid battery is designed as an absorbent glass mat battery, an absorbent microglass mat layer which serves as a separator in order to separate the negative and the positive plate and thereby prevent a short circuit between the two plates. Furthermore, the positive plate also has a positive electrode grid which is composed of lead. The positive electrode grid likewise includes an electrode contact element. The positive grid is encased by a lead oxide layer as active material, said lead oxide layer for its part being surrounded by the absorbent microglass mat layer. The glass-fiber separators bind the electrolyte, the sulfuric acid, so that it is no longer moveable, that is to say cannot flow out.
As an alternative, a lead-acid battery may also be in the form of a wet-cell battery. In this case, the described absorbent glass-fiber mat is dispensed with and the electrolyte, the sulfuric acid, is located in unbound form between the individual plates of the battery. Here, electrical insulation of the plates is usually performed by a separator which is composed of polyethylene. In this case, it is important that the battery does not exhibit any leaks since otherwise escaping sulfuric acid could lead both to damage inside the battery and outside the battery.
Voltages of lead-acid batteries are conventionally only measured as a total voltage. The individual voltages of the individual cells, which together form the lead-acid battery, are not measured. Therefore, fault diagnosis is made more difficult when, for example, the aim is to ascertain whether one of the individual cells of a lead-acid battery is defective and which of the individual cells of a lead-acid battery is defective.
DE 603 14 825 T2 describes an apparatus for charging and monitoring a motor-vehicle starter battery. In this case, individual voltages are tapped off. However, measurement and diagnosis take place centrally. One disadvantage of an arrangement of this kind is that openings have to be formed in the battery for the supply lines for the taps to the individual electrodes. These openings are generally susceptible to corrosion and leakages. However, leakages would lead to the problems described above. In addition, an arrangement of this kind is relatively complex in respect of manufacture since some production steps have to be modified or added. Integration into a conventional manufacturing process, and therefore industrial feasibility, is therefore possible only with difficulty and is laborious.
Consequently, the object of the invention is to develop a lead-acid battery having a plurality of individual cells, it being possible to easily monitor the function of the lead-acid battery and the lead-acid battery being easy to manufacture and at the same time being robust.
This and other objects are achieved according to the invention by a lead-acid battery having a plurality of individual cells, and a plurality of measurement circuits which are mounted on the respective individual cells in a manner integrated in the lead-acid battery. The measurement circuits are designed to measure a respective individual cell voltage. A method is also provided for measuring individual cell voltages of the lead-acid battery.
The lead-acid battery according to an embodiment of the invention has a plurality of individual cells and a plurality of measurement circuits, also called voltage measurement devices, which are mounted on the respective individual cells in a manner integrated in the lead-acid battery and which are designed to measure a respective individual cell voltage.
In the method according to an embodiment of the invention for measuring individual cell voltages of a lead-acid battery having a plurality of measurement circuits which are integrated in the battery and are arranged on the individual cells, the respective individual cell voltages are measured using the measurement circuits.
The lead-acid battery according to the invention preferably has cell connectors which electrically connect the positive electrodes and the negative electrodes of the individual cells, wherein the measurement circuits are each electrically connected to the cell connectors. The measurement circuits can be fixed, for example, on the cell connectors, also called flag connectors. Said measurement circuits can also be arranged between the flag connectors. The measurement circuits can be fixed, for example, by welding, soldering or adhesive bonding. The measurement circuits are preferably arranged on printed circuit boards which, for their part, are fixed to the cell connectors in the explained manner.
The measurement circuits each particularly preferably have at least one contact-maker which electrically contact-connects the respective measurement circuit to at least one cell connector. The contact-maker can be, for example, a flexible contact-maker. Particularly in the case of a wet-cell battery, it is advantageous when the contact-maker is acid-resistant.
In a particularly practical variant of the lead-acid battery according to the invention, the measurement circuits each comprise an energy supply interface which is electrically connected to the cell connectors.
Since the electrical voltage available from the individual cells amounts to only approximately 2 V, it is expedient that the measurement circuits each comprise a charge pump with which a supply voltage which is applied to the energy supply interface of the respective measurement circuit can be increased, since measurement circuits are usually operated with higher voltages than 2 V. As an alternative or in addition, the energy supply interface can also be electrically connected to an auxiliary battery as energy supply. As a further alternative or in further addition, the energy supply interface can be electrically connected to an inductive energy transmission component by which the measurement circuit is supplied with electrical energy in a wireless manner. In this variant of the energy supply, the electrical energy can be transmitted to the measurement circuit, for example, by use of a reading-out device. While the measurement data which is detected by the measurement circuit is detected, for example in an inductive or capacitive manner, by the reading-out device, energy is at the same time transmitted, for example in an inductive or capacitive manner, to the measurement circuit.
By way of example, the measurement circuits each include a microcontroller for processing and/or storing measurement data. A microcontroller comprises both a processor and also peripheral units on a chip and is normally matched to a specific task field. The use of the microcontroller allows efficient and cost-effective data processing. Measurement data can optionally be stored by the measurement circuit. As an alternative, measurement data can also be stored externally, that is to say outside the cells of the lead-acid battery.
The current cell voltage can be detected in a cascaded manner for example. This means that a current cell voltage is measured or detected only up to a degree of accuracy which is defined by two threshold values. In the case of this kind of data detection, data processing and transmission can be realized with a low level of expenditure or in a narrow band. As an alternative, continuous cell voltage measurement, that is to say measurement of exact voltage values of the individual cells, can also be implemented. It may possibly also suffice to provide only some of the cells with measurement circuits and to measure only the cell voltages of some of the cells. By way of example, when there are six cells, it suffices to measure only the voltage of five cells and to calculate the voltage of the sixth cell from the total voltage.
The individual measurement circuits can each include a data transmission device for transmitting measurement data in a wire-free manner. In this case, data transmission can be realized by modulation of a carrier signal with a measurement value. The type of modulation used can be, for example, amplitude modulation or frequency modulation, pulse code modulation or the like. As an alternative, data transmission can also be realized with the aid of a change in frequency. Thereby, discrete measurement values can be coded by means of frequency assignment. Cascading (combination) of measured voltage values to form voltage ranges can be realized here. These ranges are output over defined frequencies. In an alternative variant of the arrangement according to the invention, data transmission can also take place by means of Radio Frequency Identification (RFID). Using this technology, data is transmitted in a contact-free manner and without visual contact from a data carrier, the so-called transponder or tag, to an RFID reading device and vice versa. An idea on which the invention is based is carrying out the voltage measurement of the individual cell voltages without adversely affecting the encapsulation of the battery. Therefore, additional data transmission lines are advantageously avoided in line with this concept owing to the use of wire-free data transmission.
The lead-acid battery according to the invention may, for example, be in the form of a wet-cell battery, in the form of an AGM battery or in the form of a lead-gel battery. An AGM battery is intended to be understood to mean lead-acid batteries with absorbent mat separators which were discussed in detail in the introductory part. Particularly in the case of the design as an AGM battery, rapid diagnosis of a conventional lead-acid battery does not function in a reliable manner. However, reliable diagnosis can be ensured with the measurement according to the invention of individual cell voltages.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.